The flow field within the vane island passages of a centrifugal compressor diffuser is complex and includes a number of secondary flows which are a major source of energy loss. One phenomena generally regarded of importance is boundary layer separation. When the fluid next to a diffuser wall (the boundary layer) separates from the wall there is a loss in diffusing area and pressure recovery is reduced, i.e. the diffuser performance is degraded. Various attempts have been made in the past to modify the design of centrifugal compressor vane diffusers to eliminate/reduce such flow separation problems. For example, some designs include sequential sets of vane islands as well as front splitter at the leading edge of the vane islands. These designs generally increases the size of the diffuser which is a disadvantage in that it makes gas turbine engine designs more complicated and expensive.
Therefore, there is a need for a simple method of modifying the centrifugal compressor diffuser design to specifically address flow separation problems in vane island passages.